My off-the-top-of-my-head solution to Bruno Miranda's light bulb switching puzzle

lightbulbtoggle-for-brupm.rb

# http://blog.brunomiranda.com/post/5660219139/100-light-bulbs-brain-teaser

arr = Array.new(100, true)
(2..100).each do |d|
   arr.each_with_index{ |a, i| arr[i] = !a if (i + 1) % d == 0 }
end

puts arr.each_with_index.map{|a, i| i + 1 if a }.compact.join(", ")